stackframe.go

package goerr

/*
	Copyright (c) 2015 Conrad Irwin <conrad@bugsnag.com>

	Permission is hereby granted, free of charge, to any person obtaining a
	copy of this software and associated documentation files (the "Software"),
	to deal in the Software without restriction, including without limitation
	the rights to use, copy, modify, merge, publish, distribute, sublicense,
	and/or sell copies of the Software, and to permit persons to whom the
	Software is furnished to do so, subject to the following conditions:

		The above copyright notice and this permission notice shall be included
		in all copies or substantial portions of the Software.

		THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
		EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
		MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.

		IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
		CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
		TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
		SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

	https://github.com/go-errors/errors
*/

import (
	"bufio"
	"bytes"
	"encoding/json"
	"fmt"
	"os"
	"runtime"
	"strings"
)

// A StackFrame contains all necessary information about a line in a callstack.
type StackFrame struct {
	// The path to the file containing this ProgramCounter
	File string
	// The LineNumber in that file
	LineNumber int
	// The Name of the function that contains this ProgramCounter
	Name string
	// The Package that contains this function
	Package string
	// The underlying ProgramCounter
	ProgramCounter uintptr
}

// NewStackFrame populates a stack frame object from the program counter.
func NewStackFrame(pc uintptr) (frame *StackFrame) {
	frame = &StackFrame{ProgramCounter: pc}
	if frame.Func() == nil {
		return
	}
	frame.Package, frame.Name = packageAndName(frame.Func())
	frame.File, frame.LineNumber = frame.Func().FileLine(pc)
	return
}

// Func returns the function that contained this frame.
func (frame *StackFrame) Func() *runtime.Func {
	if frame.ProgramCounter == 0 {
		return nil
	}
	return runtime.FuncForPC(frame.ProgramCounter)
}

// String returns the stackframe formatted in the same way as go does
// in runtime/debug.Stack()
func (frame *StackFrame) String() string {
	str := fmt.Sprintf("%s.%s:%s:%d\n",
		frame.Package, frame.Name, frame.File, frame.LineNumber,
	)

	source, err := frame.SourceLine()
	if err != nil {
		return str
	}

	return str + fmt.Sprintf("\t%s\n", source)
}

// MarshalJSON implements the Marshaler interface
// see https://golang.org/pkg/encoding/json/#Marshaler
func (frame *StackFrame) MarshalJSON() ([]byte, error) {
	data := map[string]interface{}{
		"package": frame.Package,
		"method":  frame.Name,
		"file":    frame.File,
		"lineno":  frame.LineNumber,
	}

	if source, err := frame.SourceLine(); err == nil {
		data["src"] = source
	}

	return json.Marshal(data)
}

// SourceLine gets the line of code (from File and Line)
// of the original source if possible.
func (frame *StackFrame) SourceLine() (string, error) {
	if frame.LineNumber <= 0 {
		return "???", nil
	}

	file, err := os.Open(frame.File)
	if err != nil {
		return "", err
	}
	defer file.Close()

	scanner := bufio.NewScanner(file)
	currentLine := 1
	for scanner.Scan() {
		if currentLine == frame.LineNumber {
			return string(bytes.Trim(scanner.Bytes(), " \t")), nil
		}
		currentLine++
	}
	if err := scanner.Err(); err != nil {
		return "", err
	}

	return "???", nil
}

func packageAndName(fn *runtime.Func) (string, string) {
	name := fn.Name()
	pkg := ""

	// The name includes the path name to the package, which is unnecessary
	// since the file name is already included.  Plus, it has center dots.
	// That is, we see
	//  runtime/debug.*T·ptrmethod
	// and want
	//  *T.ptrmethod
	// Since the package path might contains dots (e.g. code.google.com/...),
	// we first remove the path prefix if there is one.
	if lastslash := strings.LastIndex(name, "/"); lastslash >= 0 {
		pkg += name[:lastslash] + "/"
		name = name[lastslash+1:]
	}
	if period := strings.Index(name, "."); period >= 0 {
		pkg += name[:period]
		name = name[period+1:]
	}

	name = strings.Replace(name, "·", ".", -1)
	return pkg, name
}